To minimize the venting of fuel vapor into the atmosphere, many present day vehicles are equipped with a fuel vapor recovery system which employs a charcoal filled vapor canister which stores fuel vapor vented from the fuel tank. The canister is connected to the intake manifold of the vehicle engine so that during operation of the engine vapor is withdrawn from the canister into the manifold for combustion in the engine.
For various reasons, the rate at which vapor is transferred from the canister to the engine for combustion must be precisely controlled, the primary reason being to avoid overly enriching the fuel mixture as controlled by the carburetor, fuel injection or other fuel system. Thus, it is customary to employ a so-called purge valve to control this flow from the storage canister to the intake manifold.
Operation of the purge valve is typically under the control of a computer programmed to open and close the canister to intake flow passage at an intermittent rate determined by various operating characteristics monitored by the computer. Essentially, the computer functions to open the flow passage at a cyclic frequency, which may be varied by the computer, for a selected portion of each cycle, which portion may also be varied by the computer. When the flow passage is so opened, flow of vapor wil be dependent upon the vacuum or negative pressure existing at that time in the intake manifold and this in turn may vary with engine speed. Thus, in addition to controlling the flow by cyclically opening the valve, the purge valve must also include some means for regulating the rate of flow while the valve is open.
The present invention is especially directed to a purge valve which incorporates a computer controlled solenoid actuated valve and a regulating valve responsive to intake manifold vacuum commonly mounted within a three part housing formed of molded plastic elements incorporating internal passages and valve seats integrally formed in the various housing components.